Spiral wound electrical heating element

ABSTRACT

An electric heating element of the type used in automobile cigar lighters, jet engine igniters and like devices, comprising a tight, spirally wound coil made of metal heater ribbon which is transversely formed to have a cross-sectional configuration similar to a stretched-out letter &#39;&#39;&#39;&#39;Z,&#39;&#39;&#39;&#39; so as to effect a nesting or interlocking of convolutions which not only provide a mutual support of the same but also a smaller coil having a higher metal density.

United States Patent Mattis Se t. 30, 1975 [54] SPIRAL WOUND ELECTRICAL HEATING 2.959.664 11/1960 Fenn 219/270 ELEMENT 2,975,262 3/1961 Schnick 1 219 270 3,161,754 l2/l964 Horwitt 219/270 [75] Inventor: Donald J. Mattis, Norwalk, Conn.

[73] Assignec: Sun Chemical Corporation, New y y y York, NY Attorney, Agent, or Firm-Cynthia Berlow [22] Flled: Nov. 6, 1974 ABSTRACT [2H Appl- 521,358 An electric heating element of the type used in autoy mobile cigar lighters, jet engine igniters and like de- 521 US. Cl 219/270; 219/552 vices. Comprising a tight, p y wound Coil made of [51] Int. Cl. E23Q 7/22 metal heater ribbon which is transversely formed to [58] Field of Search 219/260, 267, 270, 552, have a Cross-Sectional Configuration Similar to 8 2 9 553; 317 9 stretched-out letter Z, so as to effect a nesting or interlocking of convolutions which not only provide a [56] References Cited mutual support of the same but also a smaller coil hav- UNITED STATES PATENTS ing a higher metal density.

2,959,663 11 1960 Fenn 219 270 4 Claims, 10 Drawing Figures US. Patent Sept. 30,1975 Sheet 1 of 3 US. Patent Sept. 30,1975 Sheet 2 of3 3,909,587

US. Patent Sept. 30,1975 Sheet 3 of3 3,909,587

carrying cups in the lighters remained at the same origition of the original shape and alignment despite consid- SPIRAL WOUND ELECTRICAL HEATING ELEMENT BACKGROUND Electric cigar lighters, jet engineci giiit e'rs and like de- 5 vices commonly utilizespiral'wourid heating coils. The cigar lighters to which this invention relates are well known, particularly in the automotive industry where most cars'are equipped with one or more such items. In the earlier days of the automobile, automatic electric cigar, lighters consisted of a substantially cylindrical receptacle and a spring-biased removable plug which was normally seated in the receptacle, the plug having a spiral,6-vol t heating coil at its inner end. The heating coil was carried inametal cup; and was energized by depressing the plug in the receptacle to cause engagement of the metal c'up by a bimetallic contact clip which completed an electrical circuit through the coil. By the time the coil heated to its normal, tobacco-igniting temperature, the concurrently heated bimetallic clip had spread "apart, releasing the cup whereupon the plug snapped forward and broke the circuitjThe plug was with 6- or 7 -volt electrical systems, the car manufacturersadopted l4-volt system, utilizing a l2-volt battery instead of the original 6-volt size. This'nece ssitated a redesign of the cigar lighter coils, to utilize a thinner wire or ribbon of greater length. However, the coil- "nal diameter. The new co'ils were thus much less rugged, since the thinner, longer l2-volt or 14-voltribbon lacked the support and physical strengthof its 6-volt predecessors.

The change of ribbon size has been of significant importance, since the heating coil'was a particularly critical part of ear lighters. In service, the coil is repeatedly heated to a high temperature and then applied to the tips of cigars and cigarettes to light the tobacco. It is ordinarily secured only at its respectiveerids, and the relatively numerous spiral convolutionsare otherwise unsupported except for a mica, ceramic or other backing member. The'i'ibbon must be made ofthin gauge stock due to the need for compactness, since it, is required to fit within the original 6-volt size cup or in shells of even smaller diameter. And, it is subjected to various kinds of stress, shock and abuse including elevated temperatures, vehicle vibration, pressure against cigar and cigarette tips, and tapping or scraping to remove burned tobacco particle's.

Efforts have been directed toward designing the higher voltage heating coils to resist such stresses and abuse, so as to assure reliable performance and retenerable use.

It is already known that the ribbon making up the heating coil can be advantageously grooved, formed or bent laterally to give a cross-sectional configuration or contour which provides a nesting or interlocking rela- 6O 'tionship between successive convolutions. For example, US. Pat. Nos. 2,959,663 and 2,959,644 granted on Nov. 8, 1960 to L. E. Fenn show various cross-sectional configurations of a ribbon-like coil strip contemplated Moreover, the Penn proposais did not provide for a sufficiently high overall density of heater metal in the coil while at the same time retaining low cost, since the proposals which achieved high density required special costly ribbon sections of unusual, non-uniform thickness.

The requirements of ruggedness or strength, compactness and small size of heating coils also exist in the field of jet engine igniters and kindred devices. I-Iere, large units are especially undesirable, and existing voltage and current supplies are not easily changed. For such use, high metal density in the coil and reliability or performance coupled with low cost represent important considerations, in addition to small coil size.

SUMMARY The present invention obviates the disadvantages and drawbacks of prior, tight-wound spiral heating coils, and one object of the invention is to provide an improved spiral heating coil structure in which a ribbonlike metallic strip has a unique transverse configuration which makes possible an interlocking or nesting of the convolutions and a high density of heater metal in a coil of very small size, while maintaining costs at a low figure. By virtue of the provision of an angularly offset central portion, the ribbon of this invention can be wound in a tight coil which provides important advantages in design and performance that were not possible with previously known spiral wound heating coils.

A related object of the invention is to provide an im proved spiral wound heating coil as above set forth, wherein only slight transverse forming of the ribbon or strip is required to accomplish the desired result, thereby minimizing the likelihood of cracking or failure of the metal when the coil is in use.

In accomplishing the above objects, the invention provides ribbon-like wire or strip stock with an obliquely offset, integral central portion disposed between its two opposite edge portions. Preferably the planes of the respective edge portions of the ribbon stock, when the latter is viewed in section, are substantially parallel with each other, and the angular relationship between the oblique central portion and the respective edge portions is large, as for example, on the order of although this angle can be substantially increased or else reduced for specific lighter structures. The cross-sectional configuration is in general similar to that which would be obtained if a very short piece of flat strip stock were to be reversely bent, as when commencing to form the letter Z.

The formed ribbon-like metallic strip with cross section characterized by an oblique central portion is then tightly, spirally-wound to form a heating coil. The free end of the inner convolution can be secured to a center contact stud, and the free end of the outer convolution secured to the container cup. The offset, nestable cross-sectional configuration of the strip, similar to a stretched-out letter Z, in conjunction with the securing of the respective ends, enables the coil to resist axial displacement to a considerable degree when subjected to external forces.

The relatively flat angles between the offset central ribbon portion and the respective edge portions minimize transverse stretching of the metal grain structure,

as compared with low cost coil ribbons used in present commercial heating elements. Such reduced stretching permits the use of a wider range of ribbon sizes, as to width and thickness. I have found that with the foregoing construction there is thus made possible smaller coil sizes which are characterized by an appreciably longer service life.

Other features and advantages will hereinafter appear.

FIG. 1 is a view partly in side elevation and partly in axial section of an automatic electric cigar lighter embodying the improved heating coil of the invention.

FIG. 2 is a fragmentary axial sectional view, enlarged, of the heating element assemblage of the lighter of FIG. 1.

FIG. 3 is a view similar to that of FIG. 2, but illustrating another embodiment of the invention wherein the coil faces are in reversed position in the mounting cup.

FIG. 4 is a fragmentary sectional view, greatly enlarged, through several coil convolutions illustrating the stretched-out Z configuration given to the cross section of the ribbon.

FIG. 5 is a fragmentary axial sectional view, enlarged, through the heating element assemblage of an automatic cigar lighter illustrating another embodiment of the invention.

FIG. 6 is a sectional view similar to that of FIG. 5, but illustrating the heating coil positioned with its faces reversed in the mounting cup.

FIG. 7 is a fragmentary sectional view, enlarged, through several coil convolutions of the assemblage illustrated in FIG. 6.

FIG. 8 is a fragmentary radial sectional view, greatly enlarged, of a spiral heating coil illustrating yet another embodiment of the invention wherein the central portions and side edge portions of the convolutions at one coil face only are in intimate physical contact.

FIG. 9 is a fragmentary axial sectional view of a spiral wound heating coil assemblage such as is employed in igniter plugs, and

FIG. 10 is a fragmentary sectional view, greatly enlarged, of coil convolutions illustrating another embodiment of the invention characterized by a flat angularity and spacing at the front and back coil faces.

Referring first to FIG. 1, there is shown an automatic electric cigar lighter comprising a tubular well or receptacle 10 which is mounted through an opening in a dashboard or panel 12 by means of a clamping sleeve 14 engaging the backside of the panel. The receptacle 10 has a front flange 16 engaged with the front face of the panel 12, and has a threaded shell 18 at its rear on which there is screwed a reduced, threaded portion 20 of the clamping sleeve 14.

Within the receptacle 10 is an insulating block 22 which is carried at the inside of the rear receptacle wall and on which there is mounted a bimetallic contact clip 24. The clip 24 is attached to a terminal stud 26 which projects from the rear of the receptacle and is adapted for connection to the hot lead of an energizing circuit, such as the positive terminal of the car battery.

The cigar lighter includes a removable igniting unit or plug 28 comprising a body assemblage which is generally designated by the numeral 30 and which is slidably receivable in the well 10 and removable therefrom in the well-known manner. At its front the plug body assemblage 30 has a knob 32 by which it can be grasped and handled. The inner end of the assemblage 30 has a metal heating element cup 34 which is secured to the end wall of the assemblage by means of a small eyelet 36, the latter being insulated from the cup and 457,963, filed Apr. 4, 1974 and entitled Cigar Lighter Igniting Unit;" and the construction of the cigar lighter of such copending application is accordingly made a part of the present disclosure. 7

As is usual with automatic electric cigar lighters, energization of the heating element carried in the cup 34 is effected by pressing inward (or to the right as viewed in FIG. 1) the knob 32, which shifts the cup and related parts more deeply into the receptacle 10, thereby to establish electric contact between the cup 34 and the bimetallic clip 24. The cup 34, upon engagement with the bimetallic clip 24, will spread apart the arms thereof and will be yieldably retained in the deep, circuitclosing position. The circuit from the terminal stud 26 and clip 24 is thus established to the cup 34,.from whence current can flow through the heating element or coil (contained in the cup and shortly to be described) and through a central terminal stud 37 to the ground side of the circuit as represented by the well 10. and dashboard 12.

In accordance with the present invention, there is provided for disposition within the contact cup 34a novel, tightly wound spiral heating coil 40 which is formed of metal ribbon having a unique cross-sectional configuration by which the coil can have an especially small diameter and high density of heater metal. The cross-sectional configuration is such that the coil can be readily, tightly wound, being characterized by the longitudinal central portions of the ribbon when formed into convolutions being closely juxtaposed and, in some embodiments of the invention, contiguous. When viewed in cross-section, the longitudinal central ribbon portions make an acute angle with the axis of the coil. Also, side edge portions of the ribbon have an angular disposition with respect to the longitudinal central portions thereof and with the axis of the coil, enabling the coil convolutions to nest witheach other whereby they can effect a mutual support. The improved heating element coil of the invention thus can have a high degree of strength or ruggedness and high density of heater metal while at the same time being capable of a desirably small size or diameter.

Referring to FIGS. 2 and 4, the coil 40 is illustrated as comprising multiple convolutions, four of which are numbered consecutively 42, 44, 46 and 48, the crosssectional shape of said convolutions being somewhat similar to that of a stretched-out letter Z. Each coil convolution can be considered as having a central longitudinal portion 50 and integral opposite side edge portions 52, 54. When the convolutions are viewed in cross-section, the edge portions 52, 54 are seen to be angularly disposed with respect to the longitudinal central portions 50, the configuration being much like that which would be obtained if a short, piece of flat strip stock were to be reversely bent in commencing to form it into the shape of the letter Z. When the coil 40 is tightly wound, as in a suitable fixture which confines the edge portions 52, 54, the longitudinal central portions 50 of the ribbon can be brought into intimate contact with each other as illustrated in FIG. 4, and the side edge portions 52, 54 will be spaced apart'or from each other a slight amount. Such spacing can be very little, as onthe order of 0.002 0.004 inches for example.

The forming of the ribbon stock to provide the indicated cross-sectional configuration shown in FIG. 4 can be the result of a rolling operation by which suitable rollers engage opposite sides of the ribbon and work or ity of inwardly lanced supporting portions orshoulders 64 which are arranged to engage at least the outermost convolution of the coil 40 and provide a backing there for.

By virtue of the stretched-out Z-shape which the convolutions have in cross-section, together with angularity of the portions as indicated above, the convolutions can nest with each other and provide mutual support, especially if the convolutions are relatively shifted to bring angular areas in contact, whereby the coil is surprisingly rugged and able to withstand axial force, shock, vibration, etc. Not only are the inner and outer ends of the coil securely fastened to anchorage points, but also the outermost convolutions of the coil are backed and supported by the shoulders 64 in the cup. All these points of support, in conjunction with the nesting of the convolutions, result in the stress and shock resistance mentioned above. Since the central longitudinal portions of the ribbon, when it is coiled, become tightly wound and can be contiguous, as seen in FIG. 4, the coil 40 can have a relatively small diameter, generally less than coils heretofore constructed with other cross-sectional configurations such as those resembling the letter V. FIG. 4 depicts, enlarged, actual convolutions.

The coil 40 illustrated in FIG. 2 is so arranged that the outermost edge portions at the open end of the cup are of smaller diameter than the innermost edge portions facing the back of the cup. The coil can also advantageously be reversed in its placement in the cup 34 as illustrated in FIG. 3 whereby the exposed edge portions are of larger diameter than the edge portions that are located more deeply in the cup. In each instance the tightly wound coil is characterized by central portions of the convolutions being closely juxtaposed, or even contiguous. When the metal alloy of the coil contains aluminum in its make-up, such aluminum can form an insulating oxide at the surface of the ribbon after one or several heatings thereof, whereby the touching of the convolutions will not result in shortcircuiting of the turns, this phenomenon being well known in the art.

Because the contacting portions 50 of the convolutions are mostly broad and have no sharp edges such as are present at the portions 52, 54 there is less likelihood of the insulating oxide coating of the wire becoming penetrated and breaking down. Thus the present coil is more resistant to failure from short circuits than coils where sharp edges engage juxtaposed or contiguous flat surfaces.

Another embodiment of the invention is illustrated in FIGS. 5, 6 and 7, wherein parts similar to those already described have been given similar reference numbers. In these figures, the coil 40a is wound in such a manner that the edge and inner portions of the convolutions thereof make a lesser acute angle with respect to the axis of the coil, as compared with the coil 40 previously described and illustrated inFIGS. 2 and 4. For example, in FIG. 4, the central portions of the convolutions of the coil 40 form an angle with respect to the coil axis which is indicated'at 68. In FIG. 7, the angle between the central portions of the convolutions of the coil 40a and the coil axis, indicated at 70, is smaller than the angle 68 of FIG. 4. The coil 40a of FIGS. 5 and 6 is so wound as to have the smaller angularity indicated at 70 in FIG. 7, whereas the coil 40 in FIGS. 2 and 3 is wound in a manner to have the larger angularity indicated in FIG. 4. Also, the longitudinal central portions 50a of the coil 40a can be spaced apart or from each other, as indicated by the spaces 71 in FIG. 7. The side edge portions 52a and 54a can present virtually solid opposite coil faces, by virtue of the edge portions 52a being in contact with each other; the edge portions 54a optionally can likewise be in contact. The advantages of the coil 40a illustrated in FIGS. 5, 6 and 7 are similar to those already explained above in connection with the coil 40 of FIGS. 1-4.

Also, a coil having convolutions which make a smaller angle with the coil axis, like the coil 40a, can be wound to have the center portions contacting and the side edge portions spaced from each other, as in the teaching of FIGS. l-4. Such a small angle coil 40b is shown in FIG. 8, wherein center portions 50b are in contact and edge portions 52b are spaced from each other, while edge portions 54b are in contact. Also, a small angle coil 400 is shown in FIG. 10, wherein both coil faces have the edge portions of the convolutions spaced apart.

The improved heating coil of this invention can be advantageously used in connection with igniter plugs other than those utilized in electric cigar lighters. In FIG. 9 there is shown a heating coil 400 which is disposed in a tubular metal shell 74 of an igniter plug of the type used in conjunction with jet engines or kindred devices. The outer convolution 62 of the coil 400 is bonded to the inner wall of the shell 74, and the inner convolution is bonded to the head of a central terminal stud 76, which is centrally mounted in the shell 74.

As is well understood, the shell 74 can be secured to a housing, or can form part of a threaded fitting by which it is adapted to operate in conjunction with re lated equipment.

It will now be seen from the foregoing that I have provided a unique, improved spiral wound and tightly coiled heating element which can be of especially small size and have a high density of heater metal. The coiled element can have convolutions in a nesting arrangement whereby improved strength and ruggedness are had. Moreover, the ribbon stock can be readily formed by high production equipment, making for a low cost of fabrication of the coils.

Variations and modifications are possible without departing from the spirit of the invention.

I claim:

I. An electric heating element comprising, in combination:

a. a tight spiral coil of metal heater ribbon,

b. current-carrying members connected respectively to inner and outer end portions of said spiral ribbon, to enable the latter to be electrically energized,

c. the convolutions of said ribbon having a crosssectional shape in the form of a stretched-out letter Z and having, intermediate their side edges, longitudinally extending central portions which are devoid of sharp edges and contiguous with each other, and which have an insulating oxide coating and make an acute angle with the axis of the coil,

d. side edge portions of the ribbon convolutions which border said central portions at both sides of the coil making a different acute angle with the axis of the coil and being spaced apart not to exceed 0.010 inches, said central and side edge convolution portions being capable of nesting when the convolutions are relatively shifted axially whereby the coil has additional physical support.

2. An electric heating element as in claim 1, wherein:

a. one of said current-carrying members comprises a cup in which the coil is disposed,

b. said cup having integral peripheral portions adapted to engage the outermost coil convolution to provide a back-up for the coil.

3. An electric heating element comprising, in combination:

-d. side edge portions of the ribbon convolutions which border said central portions at at least one side of the coil making a different acute angle with the axis of the coil and being normally spaced apart not to exceed 0.010 inches, said central and side edge convolution portions being capable of nesting when the convolutions are relatively shifted axially whereby the coil has additional physical support.

4. An electric heating element as in claim 3, wherein:

a. one of said current-carrying members comprises a cup in which the coil is disposed,

b. said cup having integral peripheral portions adapted to engage the outermost coil convolution to provide a back-up for the coil. 

1. An electric heating element comprising, in combination: a. a tight spiral coil of metal heater ribbon, b. current-carrying members connected respectively to inner and outer end portions of said spiral ribbon, to enable the latter to be electrically energized, c. the convolutions of said ribbon having a cross-sectional shape in the form of a stretched-out letter Z and having, intermediate their side edges, longitudinally extending central portions which are devoid of sharp edges and contiguous with each other, and which have an insulating oxide coating and make an acute angle with the axis of the coil, d. side edge portions of the ribbon convolutions which border said central portions at both sides of the coil making a different acute angle with the axis of the coil and being spaced apart not to exceed 0.010 inches, said central and side edge convolution portions being capable of nesting when the convolutions are relatively shifted axially whereby the coil has additional physical support.
 2. An electric heating element as in claim 1, wherein: a. one of said current-carrying members comprises a cup in which the coil is disposed, b. said cup having integral peripheral portions adapted to engage the outermost coil convolution to provide a back-up for the coil.
 3. An electric heating element comprising, in combination: a. a tight spiral coil of metal heater ribbon, b. current-carrying members connected respectively to inner and outer end portions of said spiral ribbon, to enable the latter to be electrically energized, c. the convolutions of said ribbon having a cross-sectional shape in the from of a stretched-out letter Z and having, intermediate their side edges, longitudinally extending central portions which are devoid of sharp edges and contiguous with each other, and which have an insulating oxide coating and make an acute angle with the axis of the coil, d. side edge portions of the ribbon convolutions which border said central portions at at least one side of the coil making a different acute angle with the axis of the coil and being normally spaced apart not to exceed 0.010 inches, said central and side edge convolution portions being capable of nesting when the convolutions are relatively shifted axially whereby the coil has Additional physical support.
 4. An electric heating element as in claim 3, wherein: a. one of said current-carrying members comprises a cup in which the coil is disposed, b. said cup having integral peripheral portions adapted to engage the outermost coil convolution to provide a back-up for the coil. 